3.2 Plant and Animal breeding

Question 1

Why do plant and animal breeders try and develop new and improved varieties of crops and livestock?

Answer 1

to provide sustainable food sources

they do this by manipulating or changing the heredity/genetics of an organism

Question 2

REMEMBER!

Answer 2

discrete variation - can divide members of a species into distinct groups
continuous variation - changes gradually from one extreme to another

Question 3

What does single gene inheritance control?

Answer 3

controls characteristics which show discrete variation

Question 4

what is polygenic inheritance?

Answer 4

characteristics which show continuous variation are controlled by several genes.
characteristics which are controlled by polygenic inheritance can also be influenced by the environment

Question 5

REMEMBER!

Answer 5

Genetically modified organisms have been reprogrammed by genetic engineering to develop characteristics that are useful to humans

Question 6

Genetic modification

reason for altering genetics, the benefit and an example

Answer 6

increase in yield - more food produced - barley
increase in nutritional value - increase in protein content - rice
resistance to disease - crop not damaged by disease - blight resistant potatoes
resistance to pests - crop resistant to insect, fungus or worms - soya been resistance
to survive a particular environment - adapted to grow in a hot, dry environment - corn
to make it more suitable for rearing or harvesting - a more uniform crop height makes harvesting easier, increasing yield - wheat

Question 7

What is a cultivar?

Answer 7

a cultivar is a plant that has been created or selected intentionally for desirable characteristics that can be maintained by cultivation.
A cultivar is different from others in at least one characteristic or trait.

Question 8

Example of cultivar?

Answer 8

agricultural crops are almost exclusively cultivars

Question 9

What is a field trial?

Answer 9

an experimental investigation in an organisms natural environment ( rather than in the lab)

Question 10

Use of field trials?

Answer 10

plant field trials used to see whether a particular treatment makes a difference to the crop
measurements such as height, grain size, yield or incidence of disease can be used to determine the effects of a treatment

Question 11

Trials can be used to evaluate what?

Answer 11

the performance of different cultivars in a range of environments
the effects of different treatments such as pesticides or fertilisers
genetically modified crops

Question 12

CHECK NOTES FOR AN EXAMPLE

Answer 12

…

Question 13

What do reliable and valid field trials require?

Answer 13

1. careful selection of treatment - if the treatment to be investigated is the effect of fertiliser, the treated plot would be given fertiliser and the control plot would have no fertiliser. all other variables would be kept constant. The treated and untreated plots should be as similar as possible (the same soil moisture and slope) to allow valid comparison of treated and untreated areas.
2. replicates - use several trial plots to increase the reliability of results. this reduces the effect of variability within samples.
3. randomisation - the treated and control areas should be scattered randomly across the site of the trial to eliminate the possibility of bias when measuring the effect of the treatment

Question 14

What is a method of increasing food security?

Answer 14

to develop new varieties of crops and livestock breeds using breeding programmes

Question 15

What do breeding programmes allow?

Answer 15

allow desirable features to be bred into particular plants or animals

Question 16

what are desirable characteristics that increase food security?

Answer 16

wheat - high grain yield
potato - resistance to fungal disease
soya bean - high protein content of seeds
strawberry - resistance to frost
dairy cattle - high milk yield
beef cattle - high meat yield

Question 17

TOPTIP

Answer 17

phenotype - physical appearance of offspring
genotype - alleles (forms of a gene) carried
dominant alleles - show up in phenotypes
recessive alleles - do not show up in phenotype unless there are no dominant alleles present to make them

Question 18

TOPTIP

Answer 18

an organisms genotype is homozygous when it has two identical alleles of a gene it is true breeding

when it has two different alleles of a gene it is heterozygous

Question 19

What are dwarf varieties of cereal?

Answer 19

dwarf varieties of some cereal crops with much shorter stems then normal were discovered
these plants put more energy into creating see and were easier to harvest, thus increasing the yield of these crops and improving food security

Question 20

What is selective breeding?

Answer 20

plant and animal breeders choose the parent organisms with the desired characteristics and use them in their breeding programme
the aim is to produce offspring with the combined characteristics of the two parents

Question 21

What is outbreeding?

Answer 21

outbreeding is the mating of unrelated or distantly related members of a species.
animals and cross pollinating plants are naturally outbreeding

Question 22

What is inbreeding?

Answer 22

inbreeding is the mating of closely related individuals

this can happen naturally in self pollinating plants

Question 23

what are inbreeding programmes?

Answer 23

in inbreeding programmes, selected plants or animals are bred for several generations until the population breeds due to the elimination of heterozygotes

Question 24

What is inbreeding depression?

Answer 24

inbreeding results in homozygosity leading to the accumulation of harmful (deleterious) homozygous alleles and increasing the chances of offspring being affected by recessive traits - this is inbreeding depression

Question 25

What can inbreeding depression result in?

Answer 25

loss of vigour and poor general health, reduced fertility or yield

Question 26

What plants are less susceptible to inbreeding depression?

Answer 26

self pollinating plants since natural selection eliminates the deleterious alleles over many generations

Question 27

How do breeders avoid inbreeding depression in naturally outbreeding species?

Answer 27

by choosing parents with desired characteristics but which are otherwise genetically diverse

Question 28

What is crossbreeding?

Answer 28

when a plant or animal is crossed with another organism with a different, but desired genotype, creating offspring with traits from both parents, improving characteristics and producing F1 organisms with hybrid vigour

Question 29

What are F1 hybrids?

Answer 29

an F1 hybrid is the cultivar derived from two different parent cultivars
e.g. almost all modern cultivars of edible (seedless) bananas are hybrids of two wild banana species with seeds

Question 30

What are disadvantages of F1 hybrids?

Answer 30

a disadvantage of F1 hybrids is the greater cost of seeds
this is because it can take several years to produce inbred lines and non commercial self-pollination often has to be done manually which is time consuming

Question 31

What is a crossbreed?

Answer 31

a crossbreed is the result of breeding two different purebred parents of different breeds

Question 32

Example of crossbreeds?

Answer 32

Scottish half bred sheep
cross between a cheviot and border leicester breeds
has the large body from border leicester and high muscle mass from cheviot

Question 33

What is mutation breeding?

Answer 33

mutation breeding in plants involves exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to breed with other cultivars

Question 34

How has mutation breeding improved certain crops?

Answer 34

giving disease resistance, dwarf habit or a change in the chemical or nutritional plant composition

Question 35

TOP TIP

Answer 35

genetically true breeding animals command higher market prices when sold as breeding stock

Question 36

What is a testcross?

Answer 36

a testcross is used to determine the genotype of an individual with a dominant phenotype to find out if it is homozygous or heterozygous
the organism with the dominant phenotype is crossed with an organism that is homozygous recessive for the same characteristic

Question 37

Why can a testcross be used in a breeding programme?

Answer 37

to identify unwanted individuals with heterozygous recessive alleles

Question 38

DONT FORGET

Answer 38

genetic engineering is the genetic alteration of a cell by insertion of a gene or genes from another organism this cell has been GM modified producing a GM organism

Question 39

What is a genome?

Answer 39

an organisms genome is the full and unique set of genetic instruction in its DNA

Question 40

What is genomic sequencing?

Answer 40

is a process which can determine the DNA sequence of an organism’s genome

Question 41

How is the DNA broken up?

Answer 41

using enzymes

Question 42

Why are genomic sequencing machines used to sequence the DNA fragments and computer programmes are used?

Answer 42

to compare the overlapping sections to recreate the sequence of the original DNA strand

Question 43

What is the purpose of genomic sequencing?

Answer 43

allows organism with desirable genes to be identified and used in breeding programmes

Question 44

What is genetic transformation?

Answer 44

genetic transformation is the alteration of the genome of a cell by the insertion of a gene or genes from another organism, either naturally or artificially
the transformed genome can then be used in breeding programmes

Question 45

What are GM crops are useful for?

Answer 45

protection from threats such as low temperatures, insects and viruses
increasing nutritional value or yield
increasing tolerance of salt or drought
reducing the need for as much fertiliser or pesticide

Question 46

What is BT toxin?

Answer 46

the soil bacterium bacillus thuringiensis (Bt) produces a protein (Bt toxin) which is toxic to certain insects
when eaten the toxin is activated and destroys the insect’s gut
there are different strains of BT toxin which are effective against different insect pests
Scientists can remove the BT toxin gene from bacteria and insert it into plants, allowing plants to produce their own toxin which offers protection against damage by insects
this removes the need to use chemical insecticides

Question 47

What is glyphosphate?

Answer 47

Glyphophate is a herbicide (weedkiller) which is particularly effective against broadleaf weeds and grasses that compete with crops
It us an enzyme inhibitor in the production of amino acids and when absorbed through the plant foliage, it is transported to the growing points of the plant, killing it.
Genetically engineered plants that are glyphosphate tolerant can ow be produced
they contain a glyphosphate resistance gene allowing farmers to control weeds without damaging their crop

Question 48

What vitamin is low in rice?

Answer 48

Rice is low in vitamin A so in areas where rice is the staple diet vitamin A deficiency and its associated visual defects are prevalent

Question 49

What can be done to sort this deficiency of vitamin A in rice?

Answer 49

two genes coding for beta carotene can be inserted into the normal rice genome so that rice plants can make beta carotene which allows us to make vitamin A.

Question 50

What is golden rice?

Answer 50

golden rice is a genetically engineered rice cultivar which contains beta carotene and therefore is yellow-orange in colour